Sodium
Phosphate Loading
This month's Performance Tips
looks at the subject of Sodium Phosphate loading. About a year ago, an article
in the Performance Matters section of Cycling Weekly suggested that sodium
phosphate loading could increase time trial performance. The article said
that 25 mile time could be reduced by about 8 % with phosphate, which, is
a hefty increase in performance. In contrast, the hormone erythropoietin (EPO)
can boost performance around 10 %.
This article is for educational
purposes only. Before, embarking on any exercise regimen you should be fit,
healthy and free from any illness/disease. If you have any queries or are
not sure about your general health and well being, you should contact your
health care advisor/family physician.
Introduction
As a sport scientist, I decided
to investigate the effects of sodium phosphate loading for my thesis. However,
I decided to examine the effects of phosphate loading on a 10 mile performance
trial on the Kingcycle ergometer, as this had not been previously researched.
Background
Whilst reviewing the literature
it became apparent that very little research had been carried out on phosphate
loading, and a lot less on the various phosphates and performance. There were
approximately only ten previous studies on phosphate and performance, and
results from these were equivocal. Several studies had shown an improvement
in VO2 max of around 10 %, whilst others showed no improvements.
Previous in vitro and in vivo
research suggested that phosphate loading altered blood biochemistry and increased
the concentration of haematological parameters such as 2,3-Diphosphoglycerate
(2,3-DPG) and intracellular inorganic phosphorous (Pi).
The delivery of oxygen to the
tissues is characterised by the oxygen - haemoglobin (O2) dissociation curve.
This curve has a vague 's' shape and can be altered under various conditions.
For instance, the curve can be right shifted with increases in i) temperature,
ii) CO2, iii) lactic acid and iv) 2,3-DPG. If the O2 curve is right shifted,
there is a greater unloading of oxygen at the venous end of the capillaries,
allowing the muscles to utilise more oxygen.
Other recent research has suggested
that phosphate loading increases both cardiac output and VO2 during exercise
which would suggest that oxygen unloading is decreased. However, this study
showed the largest improvements in performance and therefore, the exact mechanisms
for phosphate working are not yet known.
Several studies have shown no
improvement in performance, whilst other studies have shown an increase in
VO2 max of around 10 %. Only one previous study has actually shown an improvement
in time trial ability. This study consisted of cyclists riding a 40 km trial
in the laboratory after previously consuming either the placebo or phosphate
in a double blind manner for five days. Subjects in the study improved their
40 km time by 3.5 minutes, increased their VO2 max 10 % and increased their
power output by 17 %.
Phosphate has also been examined
in anaerobic tests (30 second Wingate sprint) and whilst the phosphate elevated
the cyclists' blood phosphate levels it had no effect on Wingate performance
or repeated Wingate trials. However, the phosphate used in this trial was
dibasic sodium phosphate and this is known to alter the ratio of dibasic and
monobasic phosphate (plasma phosphate). Whilst dibasic phosphate may increase
the removal of lactic acid, the consequence of lowering the dibasic / monobasic
ratio may directly contribute to fatigue at the actomyosin ATPase level, which
suggests that dibasic sodium phosphate is not ergogenic.
Studies that have shown no improvement
in any performance measure, have still been shown to alter physiological parameters,
such as altering blood biochemistry and decreasing cardiac output (amount
of blood pumped out of the heart) at a given workload and therefore, might
still be ergogenic.
Present Study
The present study used six well trained cyclists (all subjects had beaten
23 minutes for a 10) and the average personal best was 22mins 24secs. Average
VO2 max was 4.52 l·min-1, whilst average maximum aerobic power was
444 W measured on a Kingcycle ergometer. Subjects took the placebo or phosphate
(1g four times a day) for six days.
The subjects carried out a control,
placebo and phosphate trial. The control trial averaged 21min51sec (322 W),
the placebo trial was 21min58 sec (317 W) and the phosphate trial was completed
in an average of 21min14sec (344 W). As can be seen subjects improved around
40 seconds, which is a large improvement and represents around an 8 % increase
in power. One subject, however, went backwards when using the phosphate, which
means that the average improvement was actually greater than 40 seconds. During
the trials, subject's heart rates, lactate and their perceptions of effort
were not altered. Therefore, phosphate loading increased performance whilst
eliciting similar metabolic demands. This could suggest that VO2 max was increased
with phosphate loading and supports other recent studies.
Table: Showing selected results
from the three conditions
| Condition |
Power(Watts) |
Time
(Mins) |
VO2
(l min -1)
|
Heart
Rate
(b min -1) |
| Control |
322
± 36 |
21.51
± 0.55 |
3.99
± 0.29 |
179
± 5 |
| Placebo |
317
± 38 |
21.58
± 1.03 |
3.95
± 0.31 |
177
± 6 |
| Phosphate |
344
± 46 a,b |
21.14
± 1.02 a,b |
4.14
± 0.27 c |
178
± 4 |
a = Significantly different (p <= 0.05) from control
b = Significantly different (p <= 0.05) from placebo
c = Not significantly different, but tends toward significance (p = 0.07)
Conclusion
It is possible that phosphate loading might have differing effects on events
that require different exercise intensities (e.g. 10's, 25's, and 50's), although
research has not actually tested this theory. In the near future, I hope to
be investigating the effects of phosphate loading on differing aspects of
exercise and performance and in subjects of different abilities (fit, trained,
elite, men, women, young and old).
In conclusion, current research
suggests that phosphate loading increases performance in men in maximal and
endurance exercise and has been shown to increase performance in 10's, 25's
and max tests. A possible side effect of phosphate loading is that of gastrointestinal
distress, which resulted in one subject vomiting after taking the phosphate.
However, the exact mechanisms that cause these improvements have yet to be
fully elucidated.
References
1. Cade, R., Conte, M., Zauner, C., Mars, D., Peterson, J., Lunne, D., Hommen,
N., and Packer, D. (1984). Effects of phosphate loading on 2,3
diphosphoglycerate and maximal oxygen uptake. Medicine and
Science in Sports and Exercise. 16 (3) : 263 - 268.
2. Kraemer, W. J., Gordon, S. E., Lynch, J. M., Pop, M. E. M. V., and Clark,
K.
L. (1995). Effects of multibuffer supplementation on acid - base
balance and 2, 3-DPG following repetitive anaerobic exercise.
International Journal of Sports Nutrition. 5 : 300 - 314.
3. Kreider, R. B., Miller, G. W., Schenck, D., Cortes, C. W., Miriel, V.,
Somma,
C. T., Rowland, P., Turner, C., and Hill, D. (1992). Effects of
phosphate loading on metabolic and myocardial responses to maximal
and endurance exercise. International Journal of Sports Nutrition.
2 : 20 - 47.
4. Stern, R. A. (1998). Effects of sodium phosphate loading on 10 mile cycle
time trial performance. Unpublished thesis. University of Brighton.
5. Stewart, I., McNaughton, L., Davies, P., and Tristram, S. (1990). Phosphate
loading and the effects on max in trained cyclists. Research Quarterly
For Exercise And Sport. 61 (1) : 80 - 84.
